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A whistle of frequency 540 H(Z) rotates ...

A whistle of frequency `540 H_(Z)` rotates in a circle of radius `2 m`at a linear speed of `30 m//s` . What is the lowest and highest frequency heard by an observer a long distance away at rest with respect to the centre of circle ? Take speed of sound of sound in air as `330 m//s`. Can the apparent frequency be ever equal to actual ?

Text Solution

Verified by Experts

Apparent frequency will be minimum when the source is at N and moving away from the observer.

Apparent frequency will be maximum when source is at L and approaching the observer
`f_(max)=((V)/(V-V_(S)))f=((330)/(330-30))(540)=594Hz`
Further when source is at M and K, angle between velocity of source and line joining source and observer is `90^(@) or V_(s) cos theta=V_(s) cos90^(@)=0`
So, there will be no Doppler effect.
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